Number of order-8 ribbon tilings for an 8 X n strip.

Terms

a(0) =1a(1) =2a(2) =6a(3) =24a(4) =120a(5) =720a(6) =5040a(7) =40320a(8) =181440a(9) =846720a(10) =4097520a(11) =20560176a(12) =106949304a(13) =576591048a(14) =3220805709a(15) =18634276859a(16) =96125303465a(17) =497468690754